Ultra Low Phosphorus Lubricant Composition Incorporating Amine Tungstate

ABSTRACT

A low-phosphorus lubricating composition having less than 600 ppm phosphorus, comprising at least 85 weight % of a lubricating base blend, and an additive comprising the following, as a weight % of the total composition:
         (1) an amine tungstate compound at an amount which provides about 0.1 to 1400 ppm W;   (2) an alkylated diphenylamine at about 0.1-2%; and   (3) a zinc dithiocarbamate at about 0.1-2%.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns additive compositions and lubricating compositions for use in a low phosphorus environment, which provide improved resistance to lead and copper corrosion.

2. Discussion of the Prior Art

Government regulations over the last several decades have required Original Equipment Manufacturers (OEMs) to improve fuel economy and reduce pollution emissions for gasoline and diesel powered vehicles. It is common knowledge that OEMs and lubricant companies expect government to mandate even stricter fuel economy and emission requirements in the future. Many, if not all, of the vehicles now on the road contain pollution control devices to reduce pollution.

Engine oils are formulated with antioxidants, friction modifiers, dispersants and antiwear additives to improve vehicle fuel economy, cleanliness and wear. Unfortunately, many of these additives contribute to the fouling of the pollution control devices. When this occurs, vehicles emit high levels of pollution because of the failing performance of the pollution control devices.

It has been determined that high levels of phosphorus, sulfur and ash in gasoline and diesel engine oils can negatively affect the performance of pollution control devices. To ensure proper wear protection for gasoline powered engines and the pollution control equipment, GF-5, the most recent engine oil specification for gasoline powered vehicles, specifies a phosphorus range of 600 and 800 ppm.

U.S. Pat. No. 6,806,241, which is incorporated herein by reference, teaches a three-component antioxidant additive comprising: (1) an organomolybdenum compound, (2) an alklyated diphenylamine and (3) a sulfur compound being a thiadiazole and/or dithiocarbamate.

U.S. Pat. No. 7,879,777 teaches a lubricating oil composition comprising a major portion of a lubricating base oil and an antioxidant additive at about 0.1-1.5 mass percent, the additive comprising (a) a secondary diarylamine at about 0.5 mass percent; (b) (i) a molybdenum dialkyldithiocarbamate or molybdate ester in an amount which provides about 50 to about 200 ppm molybdenum, or (ii) an ammonium molybdate in an amount which provides about 50 ppm molybdenum; and (c) di-(C₁₁₋₁₄-branched and linear alkyl) amine tungstate or mono-succinimide tungstate in an amount which provides about 100 to 500 ppm tungsten.

Molybdenum additives are well known to those skilled in the art of oil formulation to act as friction modifiers to reduce engine friction and thereby improve vehicle fuel economy. However, it is also well known that high levels of molybdenum in engine oil can cause engine corrosion and wear. When this occurs, engine life expectancy is greatly reduced.

SUMMARY OF THE INVENTION

A novel lubricant composition has been discovered that contains friction modifiers, antiwear additives, antioxidants and corrosion inhibitors with a tungsten source and low phosphorus content that offers excellent fuel economy while maintaining good corrosion and wear protection. A particular embodiment is substantially free of molybdenum. The novel lubricant composition contains 600 ppm or less of phosphorus and 800 ppm or less of tungsten. It can be used as a top treat to existing fully formulated gasoline or diesel engine oils or combined with one or more dispersants, detergents, VI improvers, base oils and any other additive(s) needed to make fully formulated engine oil.

An embodiment which achieves the desired result is a lubricating composition comprising at least 85 weight percent of a base blend blend, and the following additive, based on weight percent of the total lubricating composition:

(1) an tungstate salt, preferably an amine tungstate, at an amount to provide 0.1 to 1400 ppm W, preferably 200 to 1200 ppm W. (2) an alkylated diphenylamine, at about 0.1-2.0%, preferably 0.5-1.5%; and (3) a dithiocarbamate, at about 0.1-2.0%, preferably 0.50-1.5%.

Preferably, the lubricating composition is substantially free of molybdenum.

DETAILED DESCRIPTION OF THE INVENTION (1) Tungstate Salts

(a) Amine Tungstates

Amine tungstates are known to those skilled in the art. As non-limiting examples, U.S. Pat. No. 7,335,625 and U.S. Pat. No. 7,879,777, incorporated herein by reference, teach the reaction product of a metal acid hydrate of formula MO₄H₂.H₂O with at least one alkyl amine, having the formula:

wherein M is tungsten; and R¹ and R² may be identical or different, and are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C₂-C₄₀ alkyl, C₃-C₄₀ cycloalkyl, C₆-C₄₀ aryl, C₇-C₄₀ alkaryl and aralkyl. In a preferred embodiment, the products are a di-(C₁₁₋₁₄-branched and linear alkyl) amine tungstate or a mono-succinimide tungstate.

Additional amine tungstates are set forth in US Published Application No. 2008/0234154, incorporated herein by reference, which teaches an organic tungsten complex prepared by reacting

-   -   (a) an ammonium tungstate salt, wherein the tungstate salt is         the reaction product of an acidic tungsten and a nitrogenous         base; and     -   (b) a fatty acid derivative comprising one or more of         -   (i) a reaction product of (A) a secondary amine and (B) a             fatty oil or a fatty acid,         -   (ii) a monoglyceride and/or di-glyceride.

A preferred amine tungstate is dialkylammonium tungstate, as exemplified in Table 1, available as Vanlube® W 324 from R.T. Vanderbilt Company, Inc.

(b) Other Tungsten-Containing Compounds

Other compounds which may be effective in providing tungsten to the present invention include a soluble tungstate salt prepared, most commonly through the incorporation of alkylammonium cations; ammonium 4-t-butyl catechol vanadate and tungstate salts; tungsten carboxylates; diarene tungsten tricarbonyl, arene tungsten, or a dichlorotetranaphthyloxy tungsten; trinuclear thiotungstate; tungsten dialkyldithiophosphate; tungsten dithiocarbamates.

As set forth in US Published Application No. 2008/0234154, incorporated herein by reference, an organic tungsten complex may be prepared by reacting a tungsten salt and a fatty acid derivative, wherein the tungsten salt is the reaction product of an acidic tungsten and a nitrogenous base. These compositions contain an organic tungsten complex defined as either the reaction product of a mono- or diglyceride and a tungsten source, or as the reaction product of a secondary amine, a fatty acid derivative, and a tungsten source.

(2) Alkylated Diphenyl Amines (ADPA)

Alkylated diphenyl amines are widely available antioxidants for lubricants. One possible embodiment of an alkylated diphenyl amine for the invention are secondary alkylated diphenylamines such as those described in U.S. Pat. No. 5,840,672, which is hereby incorporated by reference. These secondary alkylated diphenylamines are described by the formula X—NH—Y, wherein X and Y each independently represent a substituted or unsubstituted phenyl group having wherein the substituents for the phenyl group include alkyl groups having 1 to 20 carbon atoms, preferably 4-12 carbon atoms, alkylaryl groups, hydroxyl, carboxy and nitro groups and wherein at least one of the phenyl groups is substituted with an alkyl group of 1 to 20 carbon atoms, preferably 4-12 carbon atoms. It is also possible to use commercially available ADPAs including VANLUBE®SL (mixed alklyated diphenylamines), DND, NA (mixed alklyated diphenylamines), 81 (p,p′-dioctyldiphenylamine) and 961 (mixed oxylated and butylated diphenylamines) manufactured by R.T. Vanderbilt Company, Inc., Naugalube® 640, 680 and 438L manufactured by Chemtura Corporation and Irganox®L-57 and L-67 manufactured by Ciba Specialty Chemicals Corporation and Lubrizol 5150A & C manufactured by Lubrizol. Another possible ADPA for use in the invention is a reaction product of N-phenyl-benzenamine and 2,4,4-trimethylpentene.

Alkylated diphenylamines, also known as diarylamine antioxidants, include, but are not limited to diarylamines having the formula:

wherein R′ and R″ each independently represents a substituted or unsubstituted aryl group having from 6 to 30 carbon atoms. Illustrative of substituents for the aryl group include aliphatic hydrocarbon groups such as alkyl having from 1 to 30 carbon atoms, hydroxy groups, halogen radicals, carboxylic acid or ester groups, or nitro groups.

The aryl group is preferably substituted or unsubstituted phenyl or naphthyl, particularly wherein one or both of the aryl groups are substituted with at least one alkyl having from 4 to 30 carbon atoms, preferably from 4 to 18 carbon atoms, most preferably from 4 to 9 carbon atoms. It is preferred that one or both aryl groups be substituted, e.g. mono-alkylated diphenylamine, di-alkylated diphenylamine, or mixtures of mono- and di-alkylated diphenylamines.

The diarylamines may be of a structure containing more than one nitrogen atom in the molecule. Thus the diarylamine may contain at least two nitrogen atoms wherein at least one nitrogen atom has two aryl groups attached thereto, e.g. as in the case of various diamines having a secondary nitrogen atom as well as two aryls on one of the nitrogen atoms.

Examples of diarylamines that may be used include, but are not limited to: diphenylamine; various alkylated diphenylamines; 3-hydroxydiphenylamine; N-phenyl-1,2-phenylenediamine; N-phenyl-1,4-phenylenediamine; monobutyldiphenylamine; dibutyldiphenylamine; monooctyldiphenylamine; dioctyldiphenylamine; monononyldiphenylamine; dinonyldiphenylamine; monotetradecyldiphenylamine; ditetradecyldiphenylamine, phenyl-alpha-naphthylamine; monooctyl phenyl-alpha-naphthylamine; phenyl-beta-naphthylamine; monoheptyldiphenylamine; diheptyldiphenylamine; p-oriented styrenated diphenylamine; mixed butyloctyldiphenylamine; and mixed octylstyryldiphenylamine.

Examples of commercially available diarylamines include, for example, diarylamines available under the trade name IRGANOX® from Ciba Specialty Chemicals; NAUGALUBE® from Crompton Corporation; GOODRITE® from BF Goodrich Specialty Chemicals; VANLUBE® from R. T. Vanderbilt Company Inc.

Another class of aminic antioxidants includes phenothiazine or alkylated phenothiazine having the chemical formula:

wherein R₁ is a linear or branched C₁ to C₂₋₄ alkyl, aryl, heteroalkyl or alkylaryl group and R₂ is hydrogen or a linear or branched C₁ to C₂₋₄ alkyl, heteroalkyl, or alkylaryl group. Alkylated phenothiazine may be selected from the group consisting of monotetradecylphenothiazine, ditetradecylphenothiazine, monodecylphenothiazine, didecylphenothiazine, monononylphenothiazine, dinonylphenothiazine, monoctylphenothiazine, dioctylphenothiazine, monobutylphenothiazine, dibutylphenothiazine, monostyrylphenothiazine, distyrylphenothiazine, butyloctylphenothiazine, and styryloctylphenothiazine.

(3) Dithiocarbamate

(i) Ashless Bisdithiocarbamate

The bisdithiocarbamates of formula II are known compounds described in U.S. Pat. No. 4,648,985, incorporated herein by reference:

The compounds are characterized by R⁴, R⁵, R⁶ and R⁷ which are the same or different and are hydrocarbyl groups having 1 to 13 carbon atoms. Embodiments for the present invention include bisdithiocarbamates wherein R⁴, R⁵, R⁶ and R⁷ are the same or different and are branched or straight chain alkyl groups having 1 to 8 carbon atoms. R⁸ is an aliphatic group such as straight and branched alkylene groups containing 1 to 8 carbons.

A preferred ashless dithiocarbamate is methylene-bis-dialkyldithiocarbamate, where alkyl groups contain 3-16 carbon atoms, and is available commercially under the tradename VANLUBE® 7723 from R.T. Vanderbilt Company, Inc.

The ashless dialkyldithiocarbamates include compounds that are soluble or dispersable in the additive package. It is also preferred that the ashless dialkyldithiocarbamate be of low volatility, preferably having a molecular weight greater than 250 daltons, most preferably having a molecular weight greater than 400 daltons. Examples of ashless dithiocarbamates that may be used include, but are not limited to, methylenebis(dialkyldithiocarbamate), ethylenebis(dialkyldithiocarbamate), isobutyl disulfide-2,2′-bis(dialkyldithiocarbamate), hydroxyalkyl substituted dialkyldithiocarbamates, dithiocarbamates prepared from unsaturated compounds, dithiocarbamates prepared from norbornylene, and dithiocarbamates prepared from epoxides, where the alkyl groups of the dialkyldithiocarbamate can preferably have from 1 to 16 carbons. Examples of dialkyldithiocarbamates that may be used are disclosed in the following patents: U.S. Pat. Nos. 5,693,598; 4,876,375; 4,927,552; 4,957,643; 4,885,365; 5,789,357; 5,686,397; 5,902,776; 2,786,866; 2,710,872; 2,384,577; 2,897,152; 3,407,222; 3,867,359; and 4,758,362.

Examples of preferred ashless dithiocarbamates are:

Methylenebis(dibutyldithiocarbamate), Ethylenebis(dibutyldithiocarbamate), Isobutyl disulfide-2,2′-bis(dibutyldithiocarbamate), Dibutyl-N,N-dibutyl-(dithiocarbamyl)succinate, 2-hydroxypropyl dibutyldithiocarbamate, Butyl(dibutyldithiocarbamyl)acetate, and S-carbomethoxy-ethyl-N,N-dibutyl dithiocarbamate. The most preferred ashless dithiocarbamate is methylenebis(dibutyldithiocarbamate).

(ii) Ashless Dithiocarbamate Ester.

The compounds of formula III are characterized by groups R⁹, R¹⁰, R¹¹ and R¹² which are the same or different and are hydrocarbyl groups having 1 to 13 carbon atoms. VANLUBE® 732 (dithiocarbamate derivative) and VANLUBE® 981 (dithiocarbamate derivative) are commercially available from R.T. Vanderbilt Company, Inc.

(iii) Metal Dithiocarbamates.

The dithiocarbamates of the formula IV are known compounds. One of the processes of preparation is disclosed in U.S. Pat. No. 2,492,314, which is hereby incorporated by reference. R¹³ and R¹⁴ in the formula IV represent branched and straight chain alkyl groups having 1 to 8 carbon atoms, M is a metal cation and n is an integer based upon the valency of the metal cation (e.g. n=1 for sodium (Na⁺); n=2 for zinc (Zn²⁺); etc.).

A preferred metal dithiocarbamate is zinc diamyldithiocarbamate, available as Vanlube® AZ, but may also be zinc dibutyldithiocarbamate or piperidinium pentamethylene dithiocarbamate

The components of the additive compositions of the invention can either be added individually to a base blend to form the lubricating composition of the invention or they can be premixed to form an additive composition which can then be added to the base blend. The resulting lubricating composition should comprise a major amount (i.e. at least 85% by weight) of base blend and a minor amount (i.e. less than 10% by weight, preferably about 2-5%) of the additive composition.

In order to satisfy the desire of industry to have an ultra-low phosphorus lubricating composition, the phosphorus level should be less than 600 ppm, preferably less than 300 ppm. The phosphorus may be provided in the form of zinc dialklydithiophosphate (ZDDP), in either conventional or fluorinated form (F-ZDDP), or as any ashless phosphorus source. It is also noted that while the inventive additive composition works to surprisingly reduce corrosion in ultra-low phosphorus oils, use of the additive composition is contemplated for base oils regardless of the phosphorus level.

Zinc dialkyl dithiophosphates (“ZDDPs”) are also used in lubricating oils. ZDDPs have good antiwear and antioxidant properties and have been used to pass cam wear tests, such as the Seq. IVA and TU3 Wear Test. Many patents address the manufacture and use of ZDDPs including U.S. Pat. Nos. 4,904,401; 4,957,649; and 6,114,288. Non-limiting general ZDDP types are primary, secondary and mixtures of primary and secondary ZDDPs. mixtures of primary and secondary ZDDPs and low volatility phosphorous compounds described in, and function the same as the antiwear additives described in, the non-limiting patent applications US 2010/0062956 and US 2010/0056407. It is not necessary for the low volatility phosphorus containing antiwear additive to contain zinc. Nitrogen containing compounds can also be used in place of zinc. The terms low volatility is defined by the GF-5 specification. The GF-5 specification is the next passenger car motor oil specification which limits phosphorous volatility. Modification to this term in subsequent gasoline and diesel engine oil specifications are also included for reference. In general, any low volatile, phosphorus containing antiwear additive is suitable for use with this invention.

Base Oils

A suitable base blend is any fully formulated engine oil for any gasoline, diesel, natural gas, bio-fuel powered vehicle that is top treated with the inventive composition. A base blend can also be any partially formulated engine oil consisting of one or more base oils, dispersants, detergents, VI improvers and any other additives such that when combined with the inventive composition constitutes a fully formulated motor oil. Base oils suitable for use in formulating the compositions, additives and concentrates described herein may be selected from any of the synthetic or natural oils or mixtures thereof. The synthetic base oils include alkyl esters of dicarboxylic acids, polyglycols and alcohols, poly-alpha-olefins, including polybutenes, alkyl benzenes, organic esters of phosphoric acids, polysilicone oils, and alkylene oxide polymers, interpolymers, copolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, and the like.

Natural base oils include animal oils and vegetable oils (e.g., castor oil, lard oil), liquid petroleum oils and hydrorefined, solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of lubricating viscosity derived from coal or shale are also useful base oils. The base oil typically has a viscosity of about 2.5 to about 15 cSt and preferably about 2.5 to about 11 cSt at 100° C.

The data in Table 1 demonstrate the superior Cu/Pb corrosion protection offered by the inventive additive composition, where numbers indicate weight percent as part of the entire lubricant composition. Corrosion resistance is measured according to HTCBT, High Temperature Corrosion Bench Test (ASTM D 6594), wherein lower number indicates less corrosion. The comparative prior art compounds C1, C2 and C3 are prepared according to U.S. Pat. No. 6,806,241. The molybdenum ester/amide can be found commercially as Molyvan® 855, manufactured by R.T. Vanderbilt Company.

TABLE 1 High Temperature Corrosion Bench Test C1 C2 C3 4 Base Blend* 95.00 95.00 95.00 95.00 Base Oil** 1.40 2.00 2.00 2.05 Molybdenum ester/amide, 0.90 0.90 0.90 7.9% Mo Styryl/octyl diphenylamine 1.50 1.50 1.50 1.50 Zinc dialkyldithiocarbamate, 1.00 1.00 50% active Zinc dialkyldithiophosphate (1), 0.20 0.20 0.20 0.20 7.5% P Amine Tungstate (29.5% W) 0.25 Methylene-bis dibutyl, 0.40 0.40 dithiocarbamate TOTAL 100.00 100.00 100.00 100.00 Molybdenum content, ppm 700 700 700 0 (nominal) Tungsten content, ppm (nominal) 0 0 0 738 Phosphorus content, ppm 150 150 300 150 (nominal) HTBCT corrosion, Cu + Pb (ppm) 369 600 351 3 HTCBT Cu/Pb (ppm) 43/326 192/408 227/124 0/3 *Base blend is a GF-4 base blend including dispersant, detergent, and viscosity modifier **base oil as diluent without additives to bring the total to 100% 

1. A low-phosphorus lubricating composition having less than 600 ppm phosphorus, comprising at least 85 weight % of a lubricating base blend, and an additive comprising the following, as a weight % of the total composition: (1) a tungsten source at an amount which provides about 0.1 to 1400 ppm W; (2) an alkylated diphenylamine at about 0.1-2%; and (3) a zinc dithiocarbamate at about 0.1-2%.
 2. The composition of claim 1, wherein the tungsten source is an amine tungstate.
 3. The composition of claim 2, wherein the amine tungstate compound is an alkylammonium tungstate.
 4. The composition of claim 1, wherein the amine tungstate compound is a di-(C₁₁₋₁₄-branched and linear alkyl) amine tungstate.
 5. The composition of claim 1, wherein the tungsten source is at an amount which provides about 200 to 1200 ppm tungsten.
 6. The composition of claim 1, wherein the tungsten source is at an amount which provides about 200 to 1200 ppm tungsten.
 7. The composition of claim 1, which is substantially free of molybdenum.
 8. The composition of claim 1, wherein the additive comprises: (1) di-(C₁₁₋₁₄-branched and linear alkyl) amine tungstate which provides about 0.1 to 1400 ppm W; (2) an alkylated diphenylamine at about 0.1-2%; and (3) a zinc dithiocarbamate at about 0.1-2%; wherein the composition is substantially free of molybdenum.
 9. A method of lubricating an engine with improved inhibition of lead and/or copper corrosion, comprising using the lubricating composition of claim 1 in an engine. 